Currently, electrical insulation systems are made of anhydride-cured epoxies. The reason why electrical insulations are widely made from these materials is because they offer a good compromise between cost, electrical, mechanical and thermal properties. Anhydride cured epoxies, however, present some important drawbacks especially from an environmental point of view. The use of anhydrides is under scrutiny of different authorities and could eventually be banned in the future. Anhydride-cured epoxies also are crack sensitive materials which causes problems in various manufacturing processes.
It has now been found that poly(dicyclopentadiene), not containing or containing a filler material, can be used as an electrical insulation system for example for bushings, instruments and distribution transformers. It is curable at room temperature and easy to process. Moreover, it has been discovered that it has surprisingly good electrical properties and has a very low sensitivity to cracking due to its excellent fracture toughness. Additionally, poly(dicyclopentadiene) has surprisingly stable hydrophobic properties which makes it particularly useful for electrical outdoor applications. Dicyclopentadiene as a starting material is commercially available and cheap. It therefore offers new manufacturing possibilities which allow a decrease of production cycle time and also offers the possibility of manufacturing bulky parts with limited residual stresses.
Dicyclopentadiene as the monomeric starting material further has a low viscosity. Using such a starting material has the advantage that, due to its low viscosity, it is possible to compound the monomeric starting material with up to 85% by weight with a filler material such as silica, which is of special importance for the manufacture of filled electrical insulation parts.
The low viscosity of the starting monomer gives also the possibility to manufacture large bulky electrical insulation parts with complex shapes, e.g. via injection molding. It further opens the possibility to electrically impregnate reinforcements, like fiber fabrics or mica tapes, conventionally used in electrical insulation, which is not possible e.g. with conventional thermoplastics.